What this calculator does
A grain is a small, old unit of mass still used today in ammunition (bullet and powder weights), pharmacy and archery (arrow and bow-string weights), defined so that one avoirdupois ounce equals exactly 437.5 grains. This ounces to grains calculator converts between the two in either direction using that fixed relationship.
The easy mistake is confusing "gr" for grains with "g" for grams. They are not close: one gram is only about 15.4 grains, while one grain is a tiny fraction of a gram (roughly 0.0648 g). This calculator shows the equivalent in grams alongside the grain figure specifically so that distinction is clear rather than assumed.
The formula
To convert ounces to grains, multiply by 437.5, the exact number of grains in one avoirdupois ounce. To convert grains to ounces, divide by the same 437.5. Both directions use this single fixed constant, since it is a definition rather than a measured approximation.
| Term | Meaning |
|---|---|
| Grain (gr) | A small unit of mass, defined as exactly 1/437.5 of an avoirdupois ounce, used for bullets, gunpowder charges and archery equipment. |
| Avoirdupois ounce (oz) | The everyday ounce used for weighing most goods, equal to exactly 437.5 grains. |
| Gram (g) | The metric unit often confused with grains due to the similar abbreviation; 1 oz ≈ 28.3495 g. |
The inputs explained
| Field | What to enter |
|---|---|
| Convert | Choose whether you are converting ounces to grains or grains to ounces. |
| Value | The amount to convert, in whichever unit the direction above starts from. |
When to use it
Reading a bullet or powder weight in grains
Ammunition components are specified in grains rather than ounces or grams, so converting a familiar ounce figure into grains makes a component spec easier to compare against a target load.
Checking an archery arrow or draw weight spec
Arrow and bow-string weights are commonly quoted in grains; converting from an ounce figure on a scale reading gives the number in the unit archery suppliers actually use.
Avoiding a grams-for-grains mix-up
Seeing "gr" on a pharmacy or historical recipe measurement and mistakenly reading it as grams would produce a result many times too large; converting explicitly avoids that error.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Common ounce amounts converted to grains
A range of ounce amounts and their grain equivalents.
| Ounces | Grains | Grams (for comparison) |
|---|---|---|
| 0.5 oz | 218.75 gr | 14.17 g |
| 1 oz | 437.50 gr | 28.35 g |
| 2 oz | 875.00 gr | 56.70 g |
| 5 oz | 2,187.50 gr | 141.75 g |
| 8 oz | 3,500.00 gr | 226.80 g |
| 16 oz | 7,000.00 gr | 453.59 g |
Common grain amounts converted to ounces
A range of grain amounts, as seen on ammunition or pharmacy labels, converted back to ounces.
| Grains | Ounces |
|---|---|
| 50 gr | 0.1143 oz |
| 100 gr | 0.2286 oz |
| 175 gr | 0.4000 oz |
| 437.5 gr | 1.000 oz |
| 875 gr | 2.000 oz |
| 1750 gr | 4.000 oz |
Questions
Is "gr" for grains the same as "g" for grams?
No, and they are easy to mix up. A grain is about 0.0648 grams, so reading "gr" as grams overstates a weight by a factor of roughly 15.4.
Why is the ounce-to-grain factor exactly 437.5?
It comes from the historical definitions of the avoirdupois pound (7,000 grains) and ounce (1/16 of a pound), giving 7,000 ÷ 16 = 437.5 grains per ounce exactly, with no rounding involved.
Where are grains still used today?
Mainly in ammunition (bullet and gunpowder charge weights), pharmacy (some older dosage measurements) and archery (arrow and bow-string weights), all fields where the unit has stuck around from historical practice.
How many grains are in a pound?
Exactly 7,000 grains, since a pound is 16 avoirdupois ounces and each ounce is 437.5 grains (16 × 437.5 = 7,000).
For everyday cooking conversions between ounces and other units, see the site’s other ounce converters. To convert a plain dollar amount into cents, see the cent to dollar calculator.